In the horology field, a watch mechanism called an “escapement” has been used for centuries and its purpose is to maintain and count the oscillations of the balance wheel or of the pendulum of the timepiece. Accordingly, the mechanism periodically communicates a portion of the motive energy of a barrel, by means of a toothed wheel called an “escapement wheel” to the regulating member (balance-hair spring or pendulum) of the watch or clock. When this toothed wheel is not in motion, it is immobilized by a mobile called a “lever” or “immobilizer” depending on the type of escapement used.
The major drawback of this escapement is that the movements of said mobile take place with considerable functional clearances which negatively effects the performance of the escapement.
European patent application No. EP 2 037 335 A2 relates to a lever for a watch escapement. In FIGS. 7 and 8 of this patent application there is a representation of a lever comprising two attachment arms (numbered 7) and an elastic spring provided to be acted upon in tension (numbered 10). These three elements are linked to the connection zone (numbered 6) of the two arms (numbered 2) of the lever and they are all three situated on one and the same side of the lever. The attachment arms are identical; between them they form an acute angle and each comprise at their free end an annular eyelet (numbered 8). The spring is placed between them, at an equal distance from one and from the other, and it is furnished at its free end with an attachment plate (numbered 11) having an oblong hole (numbered 12).
Such a lever is very difficult to attach with precision. Specifically, each of the two eyelets must be attached separately and then the attachment plate must be attached, since the latter must be able to be tightened adjustably with a screw. It is also necessary to provide sufficient space around the attachment plate to be able to adjust its position. Moreover, this lever is extremely sensitive to the dimensional variations of its constituent parts, which must then have very restricted manufacturing tolerances.